SCTP: change sctp_ctl_sock_init() to try IPv4 if IPv6 fails

Change sctp_ctl_sock_init() to try IPv4 if IPv6 socket registration
fails.  Required if the IPv6 module is loaded with "disable=1", else
SCTP will fail to load.
Signed-off-by: Brian Haley <brian.haley@hp.com>
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/protocol.c

@@ -717,15 +717,20 @@ static int sctp_inetaddr_event(struct notifier_block *this, unsigned long ev,
 static int sctp_ctl_sock_init(void)
 {
 	int err;
-	sa_family_t family;
+	sa_family_t family = PF_INET;
 
 	if (sctp_get_pf_specific(PF_INET6))
 		family = PF_INET6;
-	else
-		family = PF_INET;
 
 	err = inet_ctl_sock_create(&sctp_ctl_sock, family,
 				   SOCK_SEQPACKET, IPPROTO_SCTP, &init_net);
+
+	/* If IPv6 socket could not be created, try the IPv4 socket */
+	if (err < 0 && family == PF_INET6)
+		err = inet_ctl_sock_create(&sctp_ctl_sock, AF_INET,
+					   SOCK_SEQPACKET, IPPROTO_SCTP,
+					   &init_net);
+
 	if (err < 0) {
 		printk(KERN_ERR
 		       "SCTP: Failed to create the SCTP control socket.\n");